IDE support in the JDK

## Introduction

When you are familiar with building and testing the JDK, you may want to configure an IDE to work with the source code. The instructions differ a bit depending on whether you are interested in working with the native (C/C++) or the Java code.

### IDE support for native code

There are a few ways to generate IDE configuration for the native sources, depending on which IDE to use.

#### Visual Studio Code

The make system can generate a Visual Studio Code workspace that has C/C++ source indexing configured correctly, as well as launcher targets for tests and the Java launcher. After configuring, a workspace for the configuration can be generated using:

    make vscode-project

This creates a file called `jdk.code-workspace` in the build output folder. The full location will be printed after the workspace has been generated. To use it, choose `File -> Open Workspace...` in Visual Studio Code.

##### Alternative indexers

The main `vscode-project` target configures the default C++ support in Visual Studio Code. There are also other source indexers that can be installed, that may provide additional features. It's currently possible to generate configuration for three such indexers, clangd, ccls and rtags. These can be configured by appending the name of the indexer to the make target, such as:

    make vscode-project-clangd

Additional instructions for configuring the given indexer will be displayed after the workspace has been generated.

#### Visual Studio

The make system can generate a Visual Studio project for the Hotspot native source. After configuring, the project is generated using:

    make hotspot-ide-project

This creates a file named `jvm.vcxproj` in `ide\hotspot-visualstudio` subfolder of the build output folder. The file can be opened in Visual Studio via `File -> Open -> Project/Solution`.

#### Eclipse CDT

The make system can generate an Eclipse CDT Workspace that enables Eclipse indexing for the C and C++ sources throughout the entire codebase, as well as registering all common make targets to be runnable from the Eclipse explorer. This can be done after configuring by running:

    make eclipse-native-env

After this is run, simply open and import the workspace in Eclipse through `File -> Import -> Projects from Folder or Archive` and at `Import source` click on the directory `ide\eclipse`, which can be found in the build output folder.

If this doesn't work, you can also try `File -> Import -> Existing Projects into Workspace` instead.

Setting up an Eclipse Workspace is relatively lightweight compared to other supported IDEs, but requires that your CDT installation has Cross GCC support enabled at the moment, even if you aren't cross compiling. The Visual C++ compiler is, at present, not supported as an indexer.

If desired, you can instead request make to only include indexing support for just the Java Virtual Machine instead of the entire native codebase, by running:

    make eclipse-hotspot-env

If you think your particular Eclipse installation can handle the strain, the make system also supports generating a combined Java and C/C++ Workspace for Eclipse which can then conveniently switch between Java and C/C++ natures during development by running:

    make eclipse-mixed-env

Do note that this generates all features that come with both Java and C/C++ natures.

Eclipse support in the JDK is relatively new, so do keep in mind that not everything may work at the moment. As such, the resulting Workspace also has compilation database parsing support enabled, so you can pass Eclipse the compile commands file (see below) if all else fails.

#### Compilation Database

The make system can generate generic native code indexing support in the form of a Compilation Database that can be used by many different IDEs and source code indexers.

    make compile-commands

It's also possible to generate the Compilation Database for the HotSpot source code only, which is a bit faster as it includes less information.

    make compile-commands-hotspot

### IDE support for Java code

#### IntelliJ IDEA

The JDK project has a script that can be used for indexing the project with IntelliJ. After configuring and building the JDK, an IntelliJ workspace can be generated by running the following command in the top-level folder of the cloned repository:

    bash bin/idea.sh

To use it, choose `File -> Open...` in IntelliJ and select the folder where you ran the above script.

Next, configure the project SDK in IntelliJ. Open `File -> Project Structure -> Project` and select `build/<config>/images/jdk` as the SDK to use.

In order to run the tests from the IDE, you can use the JTReg plugin. Instructions for building and using the plugin can be found here.

#### Eclipse

Eclipse JDT is a widely used Java IDE and has been for a very long time, being a popular choice alongside IntelliJ IDEA for Java development. Likewise, the JDK now includes support for developing its Java sources with Eclipse, which can be achieved by setting up a Java Workspace by running:

    make eclipse-java-env

After the workspace has been generated you can import it in the same way as you would with Eclipse CDT:

Follow `File -> Import -> Projects from Folder or Archive` and select the `ide\eclipse` directory in the build output folder to import the newly created Java Workspace.

If doing so results in an error, you can also import the JDK via `File -> Import -> Existing Projects into Workspace` as a last resort.

As mentioned above for Eclipse CDT, you can create a combined Java and C/C++ Workspace which can conveniently switch between Java and C/C++ natures during development by running:

    make eclipse-mixed-env